So far, there has been known a configuration, referred to as a site multihome, which establishes connections with a plurality of internet service providers (ISPs) and enables a subordinate's network to use a plurality of prefixes allocated from each of the ISPs. In addition, there has been known a configuration, referred to as a host multihome, which has a plurality of interfaces and acquires an address from a connection-accepting side for each of the interfaces. In the following description, a site having a side multihome configuration will be referred to as a multihoming site while a subnet (sub-network) pertaining to the multihoming side will be referred to as a site multihoming network.
First of all, referring to FIG. 30, a description will be given hereinbelow of a site multihome. FIG. 30 is an illustration of one example of a configuration of a network for explaining a site multihome according to a prior art technique.
FIG. 30 shows a site 1 which has connections with a plurality of ISPs (ISP 1 and ISP 2) and maintains a connectivity to the internet 701, which is an IP network, through these ISPs. This site 1 includes a subnet A and a subnet B. Therefore, the site 1 is a multihoming site, and the subnets A and B are site multihoming networks.
The site multihome is a technology capable of multiplexing connection routes to the internet 701, and the utilization of the site multihome allows the enhancement of the fault resistance characteristic on the connectivity from a communication node 702 within the site 1 to the internet 701. For example, the communication node 702 within the site 1 can establish a connection with the internet 701 through two ISPs of the ISPs 1 and 2 or it can make a connection through the internet 701 with a communication partner (CN: Correspondent Node) 703.
A prefix (network prefix) is advertised from each of the ISP 1 and the ISP 2 to the site 1 shown in FIG. 30 and, hence, the plurality of prefixes are available within a subnet pertaining to the site 1. Thus, for example, the communication node 702 having a connection with the subnet A can generate a plurality of addresses configured with of the prefixes of the respective ISP 1 and ISP 2.
As means whereby the communication node 702 gets the advantage based on the site multihome, there is a method of switching addresses to be used for communications as needed. The effect based on the site multihome is realizable by determining a transit ISP for a source address in the case of a transmission packet and by determining a transit ISP for a destination address in the case of a reception packet.
On the other hand, at present, in the case of the IETF SHIM6, as a means whereby a communication node which is in a multihomed condition owing to the site multihome makes a communication with a communication partner through the use of a plurality of addresses, there has been proposed a method of managing a plurality of addresses in the interior of a network layer and mapping them into a single identifier with respect to an upper layer for concealing the fact that the plurality of addresses exist (for example, see the following Non-Patent Document 1).
When a communication node transmits a packet to a communication partner by switching a source address, a need exists to previously notify a plurality of addresses to be used for the switching to the communication partner, and the Non-Patent Document 1 additionally discloses a message for the notification of the information thereon. As a method whereby a communication partner can grasp a plurality of addresses of a communication node which is a source, in addition to the method proposed by the Non-Patent Document 1, it is also acceptable to employ a method in which the notification is made in a state where a plurality of addresses are included in a message according to a different protocol, such as a binding update message based on the mobile IP disclosed in the following Non-Patent Document 2. Thus, the communication partner can recognize that, even in the case of a packet in which a different source address is set, it is a packet transmitted from the same communication node.
Meanwhile, several methods are conceivable as means whereby a communication partner determines a destination address to be set in a transmission packet. For example, there are a method of directly using, as a destination address, an address set in a source address of a packet received from a communication node which is in a multihoming condition and a method which involves using an address indicated explicitly by that communication node or using an address selected in consideration of information on address selection.
Thus, as the advantages, the utilization of the site multihome enables multiplexing the communication routes at the transmission/reception of a packet and achieves the recovery at a communication disconnection stemming from the interior of an ISP, the load distribution for the ISP or the like.
In the following description, a node which is in connection with a site multihoming network and which generates and holds a plurality of addresses configured with a plurality of prefixes (network prefixes) will sometimes be referred to as a site multihoming node.
Secondly, referring to FIG. 31, a description will be given hereinbelow of a host multihome. FIG. 31 is an illustration of one example of an arrangement of a network for explaining a host multihome according to a conventional technique. FIG. 31 shows a communication node 902 which establishes connections with subnets (subnet A and subnet B) through the use of a plurality of interfaces and maintains the connectivity with the internet 901 which is an IP network.
In this case, the host multihome signifies a configuration in which a node (which is sometimes referred to as a host multihoming node) having a plurality of interfaces holds a plurality of addresses acquired from each interface connection side. Anode (for example, the communication node 902) having such a configuration can multiplex the communication routes at the transmission/reception of a packet as well as the site multihome in a manner such that the switching among the interfaces is made for the communication with the communication partner 903, and it can provide the advantages, such as the recovery at communication disconnection stemming from interfaces, connected networks and ISPs and the load distribution.
Furthermore, a brief description will be given hereinbelow of a mobile IP disclosed in the Non-Patent Document 2. An MN (Mobile Node) which is a communication node according to the mobile IP receives, as allocation, at least one HoA (Home Address) from its own home network. In a case in which this MN moves to a different sub-network (foreign network), it acquires at least one CoA (Care-of Address) on a sub-network of the driving destination and transmits a binding update message including CoA association information as binding information indicative of the relationship between this CoA and the HoA allocated in the home network to an HA (Home Agent) in the home network. In this way, the HA receives, as proxy, a packet transmitted toward the HoA of the MN and transfers it to the CoA, which enables the MN to receive the packet addressed to the HoA even in the case of lying in a foreign network.
Moreover, in a case in which the MN has established a connection with a home network, it transmits a binding update message to an HA in this home network for making a request for the deletion of the registered CoA association information. Upon receipt of this binding update message, the HA deletes the CoA association information on the MN, it holds, and stops the proxy reception of a packet transmitted toward the HoA of the MN. In this way, the packet addressed to the HoA of the MN is received by the interface of the MN which is in connection with the home network.
A description will be given hereinbelow of a case in which a plurality of HAs have relation with an MN. As the case in which a plurality of HAs have relation with an MN, the following two cases are conceivable.
The first is a case in which a plurality of HAs exists in a home network allocated to an MN. In this case, each of the plurality of HAs is connected on the same linkage, and the MN registers the CoA association information in one of these HAs. As disclosed in the Non-Patent Document 1, the MN can acquire an address list of the HAs existing in the home network by employing a technique referred to as a DHAAD (Dynamic Home Agent Address Discovery). This technique is realizable in a manner such that the MN first transmits a request message to a home agent anycast address generated with a prefix of its own home network and, upon receipt of this request message, the HA in the home network returns a response message including an address list of the HAs to this MN. The addresses of the HAs included in the address list are arranged in the order of the priority of the respective HAs and, hence, the MN can select the appropriate HA by using the addresses in the order from the leading address.
The second is a case in which a plurality of home networks are allocated to an MN. The home network to be allocated to the MN is a network which provides an HoA of the MN and an HA made to manage this HoA, and the allocation of the plurality of home networks signifies that, since an HoA is allocated from each of the home networks, the MN holds a plurality of HoAs at the same time and an HA made to manage each of the HoAs exists on each of the home networks. As well as a communication node which is in a site multihomed condition, this MN is required to select an HoA to be set in a source address of a transmission packet, and when the MN switches the HoA as the source address to transmit a packet to a CN, it is required to notify a plurality of HoAs, which are to be used for the switching, to this CN in advance. In the second case, as well as the first case, a plurality of HAs can exist in a home network.
In addition, in a case in which an MN after movement transmits a packet to a CN without carrying out a route optimization, the MN generates a packet where its own HoA is set as a source address and transmits it in a state where it is encapsulated as an inner packet into an outer header addressed to the HA. Thus, the packet is delivered to the HA in a encapsulated condition and, after decapsulated in the HA, it is transferred to the CN. As disclosed in the Non-Patent Document 2, the destination of the outer header of this encapsulated packet should be the address of the HA which is managing the HoA set in the source address of the inner header. Therefore, in the case of an MN having a plurality of HoAs, since the HA through which the encapsulated packet passes is determined according to which of HoAs is selected as a source address of the inner packet, it is appropriate that the HoA selection is made in consideration of the condition of each of the HAs.
In a case in which a plurality of home networks allocated to an MN exist under the same management, although the MN may acquire priority information produced with respect to all the HAs existing on a plurality of home networks as the objects of comparison at a time, if a plurality of home networks which are not under the same management are allocated thereto, difficulty is experienced in acquiring the priority information, which has been produced with all the HAs being the objects of comparison, at a time, and the MN itself is required to collect the information from each of the HAs on a plurality of home networks for making the comparison therebetween. For this reason, for acquiring the information for the comparison between HAs existing on the respective home networks, the MN is required to inquire at the HAs on the respective home networks allocated thereto.
On the other hand, as in the case of the CN which is a communication node in a multihomed condition, as means whereby a CN determines a destination address to be set in a transmission packet, several methods are conceivable. For example, there are a method in which an HoA set in a source address of a packet received from an MN is directly used as a destination address and a method which involves using an address explicitly indicated by the MN or using an HoA selected in consideration of information on address selection.
In a case in which a CN transmits a packet to an MN, since the CN does not know the CoA of this MN, the CN transmits a packet in a state where an HoA is set as a destination address. The packet where the HoA of the MN is set as the destination address is proxy-received by an HA managing this HoA, and the HA encapsulates it and transmits toward the CoA of the MN. Thus, as well as a packet to be transmitted by the MN, the HA through which the packet transmitted from the CN passes becomes an HA which manages the HoA set as a destination address of a transmission packet and, hence, it is appropriate to select a destination address of the transmission packet to the MN in consideration of the HA condition. Moreover, in this case, as well as the case of the MN, there is a need for the CN to make an inquiry at an HA existing in a home network of the MN so as to acquire the information for the comparison between the HAs.
A description will be given hereinbelow of a case in which a home network to be allocated to an MN is a site multihoming network. The HoA of the MN is an address configured with a prefix advertised in a network. Therefore, in a case in which the home network is a site multihoming network, since a plurality of different prefixes are advertised in the home network, if a plurality of different prefixes in a single network are available as prefixes for the configuration of the HoA of the MN, a single home network becomes capable of allocating a plurality of HoAs to a single MN.
As well as the case of the allocation of a plurality of home networks, also in this case, the MN is required to select an HoA to be set in a source address, and the CN is also required to select an HoA to be set as a destination address. In addition, conceivable is a case in which a plurality of home networks are allocated to an MN and, of these home networks, one or a plurality of home networks are site multihoming networks. Also in this case, it is considered that the destination address selection is made by the MN and CN in a manner similar to those mentioned above.
Furthermore, a description will be given hereinbelow of a case in which an MN according to the mobile IP is a host multihoming node. As specified in the mobile IP, a home network and a foreign network exist as the connection-accepting side of an interface of the MN. This also applies to a case in which a plurality of interfaces exist, and each of the interfaces is connectable to one of the networks.
In a case in which the MN makes communications through the use of an interface which is in connection with the home network, since a home address is allocated to this interface, a communication using an HoA directly becomes feasible without utilizing the packet switching according to the mobile IP. On the other hand, if the MN makes communications through the use of an interface which is in connection with a foreign network, since a CoA which is a valid address on the foreign network is allocated to this interface, employable are a method of utilizing the mobile IP and encapsulating a packet using an HoA between an MN and an HA before the transmission/reception thereof, a method of carrying out the route optimization with respect to a CN and conducting the transmission/reception by using a CoA directly, and other manners.    Non-Patent Document 1: Erik Nordmark, Marcelo Bagnulo, “Multihoming L3 Shim Approach”, draft-ietf-multi6-13shim-00.txt, 10 Jan. 2005.    Non-Patent Document 2: Johnson, D. B., Perkins, C. E., and Arkko, J., “Mobility Support in IPv6”, RFC3775, June 2004.
However, in a case in which, even after an MN holding a plurality of HoAs has acquired a CoA to be associated with an HoA due to movement, for preventing the present position from being known, it transmits/receives all packets through an HA without notifying the CoA acquired at the movement destination to a CN, the CN cannot grasp the present connection situation of the MN (for example, whether or not the MN is moving). As disclosed in the Non-Patent Document 2, this is because the registration of binding information in the CN by the MN is made at its option.
For this reason, even in a situation where the MN is in connection with one of a plurality of home networks and is capable of directly making a communication by using an HoA allocated from this home network, there is a possibility that the CN selects an HoA allocated from a home network which is not in connection with the MN and starts the communication. In this case, a packet transmitted from the CN arrives at the MN through a home network different from the home network which is in connection with the MN, which creates a problem in that the packet transmission route becomes relatively long and a delay of the packet transmission/reception occurs.
In addition, when the MN has a plurality of interfaces and one of these interfaces is in connection with a home network, the communication becomes feasible by directly using an HoA allocated to the interface which is in connection with that home network. However, in a case in which, for utilizing a different interface connected to a foreign network, the address allocated to this interface is registered in an HA in a state associated as a CoA with an HoA allocated to the interface which is in connection with the home network, this CoA association information is held in a binding cache of the HA, and all packets transmitted to the HoA of the MN are proxy-received by the HA and transferred to the associated CoA. Moreover, likewise, also with respect to the CN, in a case in which the MN associates an address, allocated to a different interface which is in connection with the foreign network, as a CoA with an HoA allocated to an interface which is in connection with the home network and registers it in the CN, this CoA association information is held in a binding cache of the CN, and a packet transmitted from the CN to the HoA of the MN is delivered through the HA to the MN. This creates a problem in that, for the optimization of the communication route, the CN selects one to be transmitted to the CoA of the MN by use of the CoA association information.
Still additionally, since the interface connected to the home network is utilized when the CoA association information relative to the HoA is already held in the HA and/or CN as the CoA association information on the interface connected to the foreign network, if the CoA association information in the HA and/or the CN are deleted, all the packets are received by the interface connected to the home network of the MN.
For these reasons, even in a case in which communications are made by using both an interface connected to a home network and an interface connected to a foreign network, a current-status binding update message or a binding cache held by an HA and/or a CN cannot cope with the notification and maintenance of these states, the MN cannot establish a communication using simultaneously both the interface connected to the home network and the interface connected to the foreign network. In addition, in this case, since the MN has registered the CoA association information in the CN, this causes that the CN has an interpretation different from the actual condition, i.e., the CN makes a judgment that no connection with the home network takes place.
In a case in which a plurality of home networks are allocated to an MN and a CN selects an HoA in consideration of a condition of an HA of the MN when one or a plurality of home networks of these home networks are site multihoming networks, even if a plurality of HoAs are notified from the MN, the CN cannot distinguish between these HoAs being addresses in the home networks which are site multihoming networks and they being addresses in normal home networks. Accordingly, even if several HoAs of the plurality of HoAs allocated to the MN are allocated from the same home network and managed by the same HA, the CN cannot recognize this fact and, hence, there is a possibility that the CN makes a judgment that each of the HoAs is allocated from a separate home network and managed by a separate HA and makes an inquiry at the HA.
In this case, since the CN recognizes that the HAs equal in number to the HaAs of the MN exist, for example, in the case of an inquiry at the HA, the inquiry is made at the HA which is recognized as the HA corresponding to each HoA. Accordingly, the CN carries out unnecessary inquiry, such as making the same inquiry at the same HA a number of times, which creates a problem in that ineffective time and processing take place until the address selection reaches completion.
As described above, for the selection of an HoA of an MN by a CN, the CN cannot grasp the current MN connection condition and HoA allocation status, which creates a problem in that a delay of communication occurs due to undesirable HoA selection, unnecessary HA inquiry processing, or the like.
Moreover, in a case in which an MN holds a plurality of interfaces and one of these interfaces is connected to a home network while a different interface is connected to a foreign network, there is a problem in that, even if both the interface connected to the home network and the interface connected to the foreign network are available, the MN cannot utilize these at the same time on the basis of the mobile IP in the present situation.